_ techniques map plaintext elements (characters, bits) into ciphertext elements.

Question

BlackTom AI · Accepted Answer

Substitution techniques map plaintext elements (characters, bits) directly into ciphertext elements by replacing each plaintext symbol with another symbol according to a fixed system.

1. Relevant knowledge points and concepts
- Substitution cipher: a method that replaces each plaintext element (letter, bit, or group) with a corresponding ciphertext element. Examples: Caesar cipher (shift substitution), monoalphabetic substitution, homophonic substitution, and polygraphic substitution (e.g., digraph substitution).
- Transposition cipher: a method that rearranges the positions of plaintext elements without changing the elements themselves.
- Encryption: the general process of converting plaintext to ciphertext; it encompasses many techniques (including substitution and transposition) and is not a specific mapping type.
- Symmetric cryptography: describes the key relationship (same key used for encryption and decryption), not the element-to-element mapping method.

2. Step-by-step reasoning
- The sentence to complete specifically refers to techniques that map plaintext elements into ciphertext elements (a one-to-one or systematic replacement of symbols).
- Check each option:
  - Encryption: too general; encryption is the overarching process, not the specific technique of element-to-element replacement.
  - Substitution: directly describes replacing plaintext characters or bits with other characters or bits — exactly the mapping described.
  - Transposition: changes positions of existing elements but does not map them to different element values.
  - Symmetric: pertains to key usage, not to how elements are transformed.

3. Calculations/intermediate steps
- No numeric calculations are required; the logical classification above serves as the complete evaluation.

4. Why the correct answer is correct
- Substitution explicitly defines the mapping of plaintext symbols to ciphertext symbols. Each plaintext element is replaced according to a substitution rule or table, matching the phrasing “map plaintext elements (characters, bits) into ciphertext elements.”

5. Why other options are incorrect
- Encryption: too broad (umbrella term).
- Transposition: reorders elements rather than replacing them.
- Symmetric: describes key type, not mapping method.

6. Conclusion
The correct choice is Substitution, which matches the provided answer.

_ techniques map plaintext elements (characters, bits) into ciphertext elements.Single choice

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